To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
In long-Term Evolution (LTE) systems, downlink traffic can be scheduled in unit of subframe in the time domain. In a frequency division duplexing (FDD) cell or a time division duplexing (TDD) cell, a downlink subframe having a regular cyclic prefix (CP) includes 14 orthogonal frequency division multiplexing (OFDM) symbols, and a downlink subframe having an extended CP includes 12 OFDM symbols. The first n OFDM symbols in each downlink sub frame can be used for transmitting downlink control information, n is 0, 1, 2, 3 or 4. Downlink control information includes Physical Downlink Control Channel (PDCCH) and other control information. The other OFDM symbols may be used for transmitting Physical Downlink Shared Channel (PDSCH) or enhanced PDCCH (EPDCCH). A special subframe of a TDD cell includes 3 parts, i.e., a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS). Special subframes with different configurations may have different lengths of DwPTS/GP/UpPTS. Configurations may be as shown in Table 1.
In an LTE system, PDCCH and EPDCCH respectively include DCI for allocating uplink channel resources (referred to as UL Grant) and DCI for allocating downlink channel resources (referred to as DL Grant). A UE may receive DL Grant and UL Grant in public search space and UE-specific search space. DL Grant and UL Grant in the public search space can be successfully received by all of UEs, but those in the UE-specific search space can only be successfully received by respective UEs. The downlink channel may include signals in downlink physical channels, such as PDSCH, PDCCH, EPDCCH, or the like. Downlink reference signals may include downlink reference symbols for channel state measurement and downlink reference symbols for demodulation. Downlink reference symbols for channel state measurement may include Cell-specific Reference Signal (CRS), Channel State Information Reference Signal (CSI RS), or the like. Downlink reference symbols for demodulation may include CRS, Demodulation Reference Signal (DM RS) or the like.
TABLE 1Downlink is normal CPDownlink is extended CPConfigurationsUpPTSUpPTSof specialUplink isUplink isUplink isUplink issubframeDwPTSnormal CPnormal CPDwPTSnormal CPnormal CP0 6592 · Ts2192 · Ts2560 · Ts 7680 · Ts2192 · Ts2560 · Ts119760 · Ts20480 · Ts221952 · Ts23040 · Ts324144 · Ts25600 · Ts426336 · Ts 7680 · Ts4384 · Ts5120 · Ts5 6592 · Ts4384 · Ts5120 · Ts20480 · Ts619760 · Ts23040 · Ts721952 · Ts12800 · Ts824144 · Ts———913168 · Ts———
In an LTE-advanced (LTE-A) system, multiple component carriers (CC, also referred to as a cell) are aggregated to obtain larger working bandwidth, i.e., carrier aggregation (CA). The aggregated carriers constitute downlink and uplink links in the communication system, therefore larger transmission rates can be obtained. Aggregated CCs may adopt the same duplexing manner, i.e., all of the aggregated CCs may be FDD cells or be TDD cells. Alternatively, the aggregated CCs may adopt different duplexing manners, i.e., the aggregated CCs may include both FDD cells and TDD cells. A base station may configure a UE to work in multiple Cells which include a Primary Cell (Pcell) and multiple Secondary Cells (Scell).
LTE systems need more spectrum resources to meet the requirement of increasing mobile communications services. A possible solution is to deploy LTE systems on unlicensed bands. Unlicensed bands generally have already been allocated for other usages. In order to avoid interference from other LTE devices or devices of other wireless systems in an unlicensed band, an LTE base station may check the channel state before transmitting a signal. If the channel is idle, the LTE base station may start transmitting downlink channel and/or downlink reference signal. In order to enable devices of other wireless systems to have the opportunity to occupy the channel, the LTE base station may check the channel state after transmitting downlink channel and/or downlink reference signal for a period of time, and decide whether to transmit downlink channel and/or downlink reference signal according to the obtained channel state. The maximum length of time that the base station is allowed to continuously transmit downlink channel and/or downlink reference signal and signal sequence for occupying the channel is referred to as a limited maximum transmission duration 101, and the period between transmission start time 105 and transmission end time 110 is referred to as channel occupancy duration, as shown in FIG. 1. FIG. 1 is a schematic diagram illustrating an LTE FDD frame.
If the channel is not idle, the LTE base station may not start transmitting downlink channel and/or downlink reference signal.